[vsnet-grb-info 20563] GRB 180418A: Xinglong TNT optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22661
SUBJECT: GRB 180418A: Xinglong TNT optical upper limit
DATE:    18/04/19 02:51:03 GMT
FROM:    L.P. Xin at NAOC  <xlp at nao.cas.cn>

L. P. Xin,   J. Z. Yan,  J. Y. Wei,  Y. L. Qiu, J. S. Deng,  
J. Wang,  X. H. Han, X. M. Meng, C. Wu, D. TURPIN, H. L. Li report:

We began to observe GRB 180418A  (D'Elia et al., GCN 22646)  
with Xinglong  0.8-m TNT telescope, China,  at 2018-04-18, 14:23:11(UT),
about 7.8 hours after the burst.

We obtained 10  R-band images with an exposure time of 300 sec for each frame.  
The optical afterglow (Zheng & Filippenko, GCN 22647; 
Guidorzi et al., GCN 22648; Troja et al., GCN 22652; Fong et al., GCN 
22659; Malesani et al., GCN 22660 ) was not detected in our stacked image with 10*300 sec.
The 3 sigma upper limit is estimated to be about R~20 mag  calibrated 
by USNO B1.0 R2 mag at about 8.2 hours after the burst,

We acknowledge the excellent support from Xinglong staff YunPeng Wang.